This invention relates to microwave filters and, in particular, to waveguide filters employing dielectric resonators.
Prior art waveguide filters have utilized dielectric resonators by placing them inside the waveguide. Such a structural configuration has several design problems. For example, the compensation necessary to correct for the perturbation caused by a dielectric resonator within a waveguide is too large and thus results in a poor frequency match in the waveguide passband. In addition, since a frequency tuning device is generally required in a practical filter design, the addition of such a device within a waveguide causes additional perturbation to the passband performance. Also, when plural dielectric resonators are placed in the propagating waveguide exposed to each other, inter-resonator coupling results in a reduction in peak insertion loss. Since sufficient isolation between resonators cannot be achieved when plural dielectrics are exposed to each other in the waveguide, maximum peak insertion loss cannot be realized.